U.S. Pat. Nos. 4,885,565, 5,638,060, 5,977,867, US 2002/0075135 describe touch-operated apparatus having tactile feedback for a user when touched.
In U.S. Pat. No. 4,885,565 an actuator is provided for imparting motion to the CRT when the actuator is energised to provide tactile feedback.
In U.S. Pat No. 5,638,060, a voltage is applied to a piezo-electric element which forms a switch to vibrate the element to apply a reaction force to a user's finger.
In U.S. Pat. No. 5,977,867, a tactile feedback unit generates a mechanical vibration sensed by the user when the touch screen is touched with a finger or a pointer. The amplitude, vibration frequency and pulse length of the mechanical vibration are controlled, with the pulse width being long enough to be felt but short enough to terminate before the next key touch.
US2002/0075135 describes the use of a second transducer to provide a pulse in the form of transient spike to simulate a button click.